Past studies have shown that first language and second language (L2) listeners can adapt to unfamiliar L2 pronunciation. However, little is known about the process of adaptation, especially by L2 listeners. The present study examined the degree to which L2 listeners' adaptation process is influenced by speaker intelligibility and input variability. In a 2-day experiment, L2 listeners heard and transcribed short sentences five times without feedback in seven groups that differed in speaker intelligibility and input variability (between-subject). Adaptation was measured by transcription accuracy. Findings showed greater improvements for groups with high intelligibility and high input variability. In particular, exposure to multiple speakers of the same variety resulted in the largest gain. Thus, to facilitate adaptation to unfamiliar L2 pronunciation, high-intelligibility speakers and/or multiple speakers of the same language background should be used.